Stacked DRAM device and method of manufacture

ABSTRACT

A memory stack includes a number of memory dies including a master die and one or more slave dies. The slave die can be converted to a master die by further processing. The slave die includes a memory core having memory cell arrays. The slave die also includes first and second metal layers that form first and second distribution lines in the memory core, respectively. An interface circuit in the slave die is decoupled from the first and second metal layers.

CROSS-REFERENCE TO RELATED APPLICATIONS/TECHNICAL FIELD

Pursuant to 35 U.S.C. §365, this application claims priority fromInternational Application No. PCT/US2012/037664, published as WO2012/155115 A1 on Nov. 15, 2012, which claims priority from U.S.Provisional Application No. 61/485,359, filed May 12, 2011 and entitled“STACKED DRAM DEVICE AND METHOD OF MANUFACTURE”. InternationalApplication No. PCT/US2012/037664 and U.S. Provisional Application No.61/485,359 are hereby incorporated by reference in their entirety.

The disclosure herein relates to semiconductors, and more particularlyto semiconductor packages employing multiple integrated circuit chips.

TECHNICAL FIELD

The disclosure herein relates to semiconductors, and more particularlyto semiconductor packages employing multiple integrated circuit chips.

BACKGROUND

Many computer systems use dynamic random access memory (DRAM) as systemmemory to temporarily store an operating system, critical applications,and data. With widespread use of multi-core processors, particularly, inservers and workstations, higher capacity and faster memory devices areneeded to catch up with the computing power of these processors, therebyreducing the processor-memory performance gap and allowing theapplications to use the full processing speed of modern processors.

One way to narrow the processor-memory performance gap is to developinnovative technologies to enhance characteristics of DRAM chips interms of capacity and bandwidth. Yet another way is to increase storagecapacity by stacking memory chips, while using existing DRAMtechnologies. For example, in servers and storage applications, depthstacking can be used to obtain high memory densities in a smaller spaceand most likely at a lower cost. Other industrial or embeddedapplications may demand different memory requirements, but typicallyhigh-density depth stacking is needed where space is constrained,therefore requiring more memory capacity on the same or a smaller memorymodule form factor.

Stacked memory dies can be formed by mounting two or more memory dies,one on top of the other, and interconnecting them usingthrough-silicon-vias (TSVs). Conventional solutions use substantiallyidentical memory dies derived from the same mask set to form memorystacks. While these solutions allegedly work for their intendedapplications, there are a number of disadvantages associated with thesesolutions. For example, by using substantially identical dies in thestack, certain cost saving opportunities may be lost. For instance,there are some features that may only be needed on one of the memorydies of the stack. Such features may not have to be fabricated in theother memory dies of the stack. On the other hand, if some of thesefeatures are omitted on all of the dies, the substantially identicalmemory dies used in conventional memory stacks may not be viable for useas stand-alone memory devices in a cost effective manner.

Thus, the need exists for a high density memory device formed bystacking memory dies which are not substantially identical, thereforealleviating the disadvantages of the conventional solutions. Embodimentsdescribed herein satisfy this need.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the disclosure are illustrated by way of example, and notby way of limitation, in the figures of the accompanying drawings and inwhich like reference numerals refer to similar elements and in which:

FIG. 1 illustrates a memory system using a dual in-line memory module(DIMM) including memory die stacks formed by stacking master and slavememory dies according to an embodiment;

FIG. 2 illustrates a top view of a memory die stack of FIG. 1 accordingto an embodiment;

FIG. 3 illustrates a cross sectional view of the memory die stack ofFIG. 2, as viewed along line A-A′ of FIG. 2, according to an embodiment;

FIG. 4A illustrates a cross sectional view of an in-process memory dieafter formation of transistors in memory array blocks and interfacecircuit according to an embodiment;

FIG. 4B illustrates a cross sectional view of an in-process memory dieafter formation of first and second metal layers according to anembodiment;

FIG. 4C illustrates a cross sectional view of the in-process memory dieof FIG. 4B after further processing to form a slave die according to anembodiment;

FIG. 4D illustrates a cross sectional view of the in-process memory dieof FIG. 4B after further processing to form a stand-alone die accordingto an embodiment;

FIG. 4E illustrates a cross sectional view of the in-process memory dieof FIG. 4D after further processing to form a master die according to anembodiment;

FIG. 4F illustrates a cross sectional view of an in-process memory diestack after stacking the master die of FIG. 4E and the slave die of FIG.4C according to an embodiment;

FIG. 5A illustrates a schematic diagram of a multiplexer circuit used ina x16 stand-alone die according to an embodiment;

FIG. 5B illustrates a schematic diagram of a multiplexer circuit used ina x8 stand-alone die according to an embodiment;

FIG. 5C illustrates a schematic diagram of a multiplexer circuit used ina x4 stand-alone die according to an embodiment;

FIG. 5D illustrates a schematic diagram of a multiplexer circuit used inthe memory die stack of FIG. 1 according to an embodiment;

FIG. 6A illustrates a cross sectional view of a portion of a mastermemory die with a connection to a through-silicon-via (TSV) utilizingone or more third metal layers according to an embodiment;

FIG. 6B illustrates a cross sectional view of a portion of a mastermemory die with a connection to a TSV through a re-driver circuitaccording to an embodiment; and

FIG. 7 illustrates a block diagram of a computer system using the DIMMof FIG. 1 according to an embodiment.

DETAILED DESCRIPTION

Embodiments of stacked memory devices each including a number of memorydies are disclosed herein. One embodiment of a stacked memory devicecomprises a master memory die and a slave memory die. The slave memorydie includes a memory interface circuit and a memory core formed by anumber of memory cell arrays. The slave memory die further includesfirst and second low-resistance metal layers that form first and seconddistribution lines in the memory core, respectively. The memoryinterface circuit in the slave memory die is decoupled from the firstand second low-resistance metal layers. The slave memory diecommunicates with the master memory die using one or morethrough-silicon-vias (TSVs).

In a further embodiment, a memory device is described as comprising amaster memory die and a slave memory die coupled to the master memorydie in a stacked configuration. Each of the master and slave diesincludes memory core circuitry having memory cell arrays. The memorydies also include first and second low-resistance metal layers thatrespectively form first and second distribution lines in the memory coreand interface circuitry. The master memory die is further formed withone or more additional metal layers and the core circuitry of the slavememory die couples to the interface circuitry of the master die via theone or more third metal layers.

In a further embodiment, a memory module is disclosed as comprising asubstrate and a number of memory devices mounted to the substrate. Eachof the memory devices comprises a master memory die and a slave memorydie coupled to the master memory die in a stacked configuration. Each ofthe master and slave memory dies includes memory core circuitry, firstand second low-resistance metal layers, and an interface circuitry. Thememory core circuitry comprises a number of memory cell arrays. Thefirst and second low-resistance metal layers form first and seconddistribution lines in the memory core, respectively. The master memorydie is further formed with one or more third metal layers and the memorycore circuitry of the slave memory die couples to the interfacecircuitry of the master memory die via one or more of the third metallayers.

In yet another embodiment, a method of fabricating a memory die isdisclosed as comprising forming core circuitry and interface circuitryon a semiconductor substrate. The method further includes forming firstand second low-resistance metal layers including first and seconddistribution lines in a memory core circuitry area on the semiconductorsubstrate. Next, a passivation layer is formed on the secondlow-resistance metal layer. The first and second low-resistance metallayers are decoupled from the interface circuitry.

FIG. 1 illustrates a memory system using DIMM 100 including memory diestack 160 formed by stacking master and slave memory dies 122 and 124according to an embodiment. The DIMM 100 includes a number of memorydevices, such as DRAM devices, mounted on one side of a substrateforming a single-rank DIMM. Alternatively, the memory devices may bemounted on both sides of the substrate forming a dual-rank DIMM. Thememory module 100 communicates to a memory controller 140 via a memorybus 130. The memory controller 140 communicates with an interfacecircuit associated with each memory device 120. The memory controller140 includes logic circuitry that controls read, write, and refreshoperations of each memory device 120. The read and write operations maybe performed in response to requests received from a processor 150. Thememory bus 130 includes a data bus and an address/command bus, eachcomprising a multitude of data and address/command lines, respectively.The address portion of the address/command bus comprises a number ofaddress line carrying signals that identify the location of data in thememory module 100. The command portion of the address/command busconveys instructions such as read, write, and refresh commands issued bythe memory controller 140.

Each of the memory devices 120 comprises at least one memory chip, suchas a DRAM chip. Each DRAM chip may provide 4 bits (x4), 8 bits (x8), or16 bits (x16) of a 64-bit data word. For example, it takes eight x8 DRAMchips or sixteen x4 chips to provide a 64-bit word. Many single-rankDIMMs may have enough room to hold nine memory chips on one side of theDIMM, where the ninth chip is used for storing error correction code(EEC). In some applications, such as servers, several high densitymodules (e.g., 32-Gb modules) may be used. A 32-Gb module, for example,may include eight high density memory chips, such as memory devices 120,each providing 4 Gb of storage capacity. A 4-Gb memory device may bemanufactured, for instance, by forming a memory die stack comprising anumber of memory dies. For example, the memory device 120 may comprise amemory die stack 160 including a master memory die 122 (herein after“master die 122”) and one or more, such as three, slave memory dies 124(hereinafter “slave die 124”). The master die 122, as shown in FIG. 1,sits on the top of the memory die stack 160. However, after packaging,the memory die stack is coupled to a packaging substrate that holdsintegrated circuit (IC) terminals via which the memory devicecommunicates with other devices, such that the master die 122 would beat the bottom of the stack and bonded to the packaging substrate byusing, for example, a flip-chip bonding technique.

Each of the master and slave dies 122 and 124 may include a memory core,first and second low-resistance metal layers, and an interface forcommunication with the memory controller 140. In the slave die 124, theinterface is not coupled to the first and second low-resistance metallayers via any conductors on the slave die. The master and slave dies122 and 124 are interconnected by using multiple TSVs. The interfacecircuit of the master die 122 is coupled to its memory core viaconductors on the master die. The interface circuit of the master die122 is coupled to the first and second low-resistance metal layers ofeach of slave dies 124 through one or more TSVs, as will be described inmore detail below.

FIG. 2 illustrates a top view of a memory die stack 160 of FIG. 1according to an embodiment. The top view depicts the structure of themaster die 122, which is shown in FIG. 1 as the top die of the memorydie stack 160. The structures shown in the top view, except forconnection pads 270, which are only formed in the master die 122, arecommon between master and slave dies 122 and 124. Hence, when describingthese common structures, reference is made to a “memory die” instead ofthe master die 122 or the slave die 124.

The memory die comprises a memory core including a number of memoryarray blocks 250 (e.g., 16 array blocks 250.1-250.16), several supportstructures including one or more TSV support stripes 240 (hereinafter“TSV stripe 240”), one or more interface support stripes 260(hereinafter “interface 260”), multiple (e.g., four) column circuit 220,multiple (e.g., four) row circuits 210, and a multitude of TSVs 280. Thenumber of TSVs depends on the desired bandwidth of the data connection,the granularity of the addressing and commands and the operationfrequency of the signaling on the TSVs. Typical numbers are between afew hundred and a few thousand.

The memory core may include a large number of array memory cells (e.g.,four billion cells in a 4-Gb chip) arranged in a number of (e.g., 16)memory array blocks 250 (hereinafter “array blocks 250”). Each arrayblock 250 may include a multitude of (e.g., 1024) memory sub-arrays,each arranged in multiple (e.g., 512) columns and multiple (e.g., 512)rows. Each array block 250 is arranged such that it is adjacent to aportion of a row circuit 210 and a portion of a column circuit 220. Thearray blocks 250, in addition to array cells, contain other circuitriesknown as on-pitch circuitries (their numbers correspond to bit-lines orword-lines pitches) including bit-line sense amplifiers (i.e. primarysense amplifiers) and word-line drivers and decoders.

Each row circuit 210 comprises a number of circuits including, but notlimited to, word-line driver circuits, row-address decoders, andword-line redundancy circuits. Each column circuit 220 comprisesmultiple circuits including, but not limited to, column-line drivercircuits, column-address decoders, column-line redundancy circuits, andsecondary sense amplifiers, which are connected to array data lines andfurther amplify signals after the primary sense amplifiers.

The interface 260 is formed near the connection pads 270 and comprisesinterface circuitry, which among other functions, buffers the signalscommunicated between TSVs 280 and the bond pads. The interface 260comprises a number of circuits including, but not limited to, any ofinput/output (I/O) drivers, I/O receivers, re-drivers, decoders, ESDcircuits, multiplexing and data steering circuits. It is important tonote that as a distinct feature of the disclosed embodiments, theinterface 260, in the slave die 124 is not coupled to the memory core(i.e., array blocks 250). However, as will be explained in more detailwith respect to FIGS. 3 and 4, in the master die 122, the interface 260is coupled to the array blocks 250 via one or more third metal layers.

With continued reference to FIG. 2, TSV stripes 240 are formed as one ormore (e.g., two) stripes, each encompassing a number of TSVs 280. In apreferred embodiment, there are two TSV stripes 240 formed symmetricallyat approximately equal distances from the interface 260. Depending onthe application, however, the number of TSV stripes may depend on a bitwidth of the memory die stack 160. Each TSV stripe 240 comprisescircuitries that are coupled to and communicate with the array blocks250. These circuitries include, but are not limited to, circuits thatgenerate array block control signals, circuits that send and receivedata from array blocks 250, circuits that generate power for arrayblocks 250, and circuits that drive/receive TSV signals.

The connection pads 270 connect various circuits formed on the memorydevice 120 to circuits external to the device. The connection pads 270include I/O pads, power supply pads, ground pads, and the like, whichare coupled to the circuits in the interface 260 and through theinterface 260 and distribution lines formed by the third metal layers(not shown in FIG. 2) to the memory core (i.e., array blocks 250). TheI/O pads may be coupled to the memory controller 140 via terminals ofthe memory module 100.

The connection pads 270 may be of any suitable shape, such as square,round, or the like. In some embodiments, each group of connection pads270 is a stripe of connection pads that extends substantially across arespective side of the memory device 120, i.e., each stripe may form acolumn (or row, depending on orientation) across a side of the memorydevice. In some embodiments, each group of connection pads 270 islocated near the middle of memory device 120 over the interface 260,however, in other embodiments, the connection pads 270 may be locatednear an edge or anywhere else on the master die 122 of the memory diestack 160. The connection pads 270 are only formed using the third metallayers on the master die 122, which are coupled to correspondingterminals of the memory device 120 through interconnections formed inthe substrate.

Further referring to FIG. 2, the test pads 230 are used to test arrayblocks 250 and functionalities of various circuitries of the memorydevice 120. The test pads 230 are coupled by vias to first and secondlow-resistance metal layers, through which they can access groups oflines connected to various memory device circuitries, for example,master word-lines, sense amplifier control signal lines, arraydata-lines, column select lines, and signal and power distributionlines. The test pads 230 are formed both on the master die 122 and theslave dies 124. The test pads 230 are formed so that they can becontacted by a test probe on their top metal layer. This top metal layeris the second metal layer on the slave dies 124 and either the second orthird metal layer on the master die 122. After the stack has beenassembled, only the test pads 230 on the master die can be accessed. Thetest pads 230 may be of any suitable shape, such as square, round or thelike. In some embodiments test pads 230 are formed between groups ofTSVs 280 over the TSV stripe 240. A number of test pads 230 may also beformed over the interface 260, for example, near an edge of the memorydie stack 160 or other suitable position.

The TSVs 280 provide interconnections between the master die 122 and theslave dies 124. The TSVs 280 are formed in groups, in the TSV stripes240, where they are conveniently positioned near circuitries included inthe TSV stripe 240, including drivers/receivers for TSV signals. Throughthe interconnections provided by the TSVs 280, signals and dataincluding array block control signals and data can travel from one ofthe slave dies 124 to the master die 122. In the master die 122, theycan further travel to the circuitries in interface 260, which arecoupled to respective TSVs 280. These signals and data can travel, viainterconnections not shown in FIG. 2, to respective connection pads 270.More structural details of portions of the memory die stack 160 aregiven below with respect to FIGS. 3, 4, and 6.

FIG. 3 illustrates a cross sectional view of the memory die stack 160 ofFIG. 1, as viewed along line A-A′ in FIG. 2, according to an embodiment.For purpose of brevity, and considering that the slave dies 124 arestructurally similar, reference numbers for components of slave dies124, which are also common with the master die 122, are only shown onthe top slave die 124. The structural components shown by referencenumbers on the top of the master die 122 are unique to the master die122. In each memory die, various structures are formed on a top portionof the die, with the remaining portion of the die comprising a diesubstrate, which is thinned to a suitable thickness for forming thestack 160. On each memory die the largest area is occupied by the arrayblocks 250, which contain the array cells and on-pitch circuitry.

Attached to each array block 250 is the column circuit 220, whichcontains support circuits for the array block 250 and is coupled to theon-pitch circuitry (not shown). In some embodiments, the column circuit220 includes the column-line driver circuits, the column-addressdecoders, the column line redundancy circuits, and the secondary senseamplifiers. The TSVs 280 are shown to penetrate through the substrate ofevery memory die of the memory die stack 160. In the slave dies 124, theTSVs 280 are only coupled to some of the circuitries of the TSV stripes240, e.g., driver/receivers for TSV signals and some of the circuits ofthe column circuit 220, e.g., column address decoders and secondarysense amplifiers through the first and second low-resistance metallayers 251 and 252 (hereinafter “first metal 251” and “second metal 252”shown in magnified blow-up of portion 255). However, the TSVs 280 arenot coupled to the circuitries in the interface 260 of the slave dies124. As explained below, the first and second metals 251 and 252 arealso used in the support structures, such as the interface 260 and theTSV stripes 240. Typically the bottom slave die is not thinned to thesame thickness as the master and other slave dies so that the remainingthick silicon layer provides mechanical stability to the stack 160. Thisthick layer is not relevant for the electrical function of the memorystack 160 and omitted in the figures. The TSVs 280 do not need topenetrate the bottom slave die fully.

As shown in magnified blow-up of portion 255, one embodiment of thefirst and second metals 251 and 252 form first and second distributionlines in the core and are made of low-resistance conductors, such asmetals including aluminum (Al) and copper (Cu). Vias 254 couple thefirst metal layer 251 to the second metal layer 252. In the array block250, the first metal 251 is used to form master word-lines andsense-amplifier-control signal lines, whereas the second metal 252 isused to form array data-lines, column-select lines, some of the powerdistribution lines dedicated to providing power sufficient for low-speedarray testing, and interconnections between test pads 230 and thecircuitries in the array block 250. The first and second metals 251 and252 are also used in the support structures, for example, first metal251 forms the medium-distance signals lines and power distributionlines. In the support structures, the second metal 252 forms, forexample, some of the power distribution lines sufficient to providepower for low speed array testing and some long-distance signal lines.It is worth mentioning here that in most conventional memory devices allof the long distance power distribution lines and long distance signallines are formed by the second metal.

In the master die 122, a third low-resistance metal layer 370(hereinafter “third metal 370”) made of low-resistance conductors suchas metals, for example, Al or Cu is used to connect the circuitries inthe interface 260 and the connection pads 270 to the TSVs 280. The thirdmetal 370 also interconnects connection pads 270 and the circuitries inthe support structures such as TSV stripes 240 and interface 260. Insome embodiments, the third metal 370 forms power distribution linesused for normal array operation, and in high speed testing which isnormally performed after the memory die stack 160 is packaged. In someembodiments, the third metal 370 may be replaced with a redistributionlayer (RDL) which can be formed during packaging of the memory die stack160. Also shown in FIG. 3 are the insulator portions 380 formed betweenthe TSVs 280 to electrically isolate the TSVs 280 from one another.

FIG. 4A illustrates a cross sectional view of an in-process memory die410 after formation of transistors in array blocks 250 and interface 260according to an embodiment. A primary step in the process ofmanufacturing of each die in memory stack 160 of FIG. 3 is formation oftransistors in the array block 250 and interface 260 shown in thein-process memory die 410. Interconnections between the array blocks250, interface 260, and other circuits such as column circuits 220, rowcircuits 210, and TSVs of FIG. 2 are realized through metal layers shownin FIGS. 4B-4D. For simplicity, array blocks 250 and interface 260 arenot shown in FIGS. 4B-4E.

FIG. 4B illustrates a cross-sectional view of an in-process memory die420 after formation of first and second metals 251 and 252 according toan embodiment. The memory die 420 is a starting die, which can beconverted, upon further processing, to the slave die 124, the master die122, or a stand-alone die 430 of FIG. 4D. The memory die 420 includesall of the components of the slave die 124, as discussed above withrespect to FIGS. 2 and 3, except for the TSVs 280. However, for the sakeof clarity, only metal layers and the corresponding vias in a portion ofthe memory die are shown. A high resistance metal layer 412 (alsoreferred to as “metal0”), made of a high resistance metal such astungsten (W), is used to form bit-lines and local short signal or powerconnections. The first metal 251 is coupled to the metal layer 412 byvias 414. The first metal 251 is connected by a via 416 to a portion ofthe second metal 252, which can be used as a test pad to test thecircuitry coupled to the metal layer 412 and all or some of thecircuitries coupled to the first metal 251 and the second metal 252before or after fabrication of the TSV 280. Typically test circuitrywill be implemented using, as connections, only metals 412, 251 and 252to support the test of the array blocks 250 after wafer processingbefore assembly of the stack. Examples of the circuitries connected tothe first metal 251 and the second metal 252 include master word-lines,sense amplifier control signal lines, array data-lines, column selectlines, and signal and power distribution lines. The first and secondmetals 251 and 252 are typically routed perpendicular to each other.Typically, the second metal 252 is used to form longer distributionlines.

FIG. 4C illustrates a cross sectional view of the in-process memory die420 of FIG. 4B after further processing to form the slave die 124according to an embodiment. An additional process of forming the TSV 280converts the memory die 420 to the slave die 124. As seen in FIGS. 2 and3, there are a number of TSVs 280 in each slave die and in FIG. 4C, forthe sake of clarity, only one TSV 280 is shown. The TSV 280 is typicallycoupled to the second metal 252. The first metal 251, as explainedabove, is used to form distribution lines such as master word-lines,sense amplifier control signal lines and some medium distance powerdistribution and signal lines. These distribution lines are local toeach slave die 124 and do not need to be coupled to the master die 122via the TSVs. Also, the slave die 124 does not include the third metal370 and is configured to receive its operating power from the master die122 through the TSVs 280 after formation of the memory die stack (e.g.,memory die stack 160 of FIG. 1). In particular, the slave die 124 lacksany coupling between the circuitries in the interface 260 of FIG. 3 andthe first and second metals 251 and 252 and therefore from the interface260 to the array blocks 250 of the slave die 124. However, the arrayblocks 250 of the slave die are coupled by first and second metals 251and 252 to the TSV 280 and from there to the interface 260 of the masterdie 122. The slave die 124 can be used in the memory die stack 160 aftera thinning process, which removes undesired substrate material under thebottom of the TSV 280. The slave die at the bottom of the stack may notbe thinned and can provide mechanical stability to the stack.

FIG. 4D illustrates a cross sectional view of the in-process memory die420 of FIG. 4B after further processing to form a stand-alone memory die430 according to an embodiment. The stand-alone memory die 430 isfabricated by forming vias 432 and the third metal 370 (shown as havingportions 370(a) and 370(b)). The third metal 370(a) couples to thesecond metal 252 and from there to all of the circuitries that arecoupled to the second metal 252 (shown as portions 252(a) and 252(b)). Aportion of the third metal 370(b) forms the test pad for the stand-alonememory die 430 and can be used to test the circuitry coupled to themetal layer 412 and all or some of the circuitries coupled to the firstmetal 251(a) and the second metal 252(b) including master word-lines,sense amplifier control signal lines, array data-lines, column selectlines, and signal and power distribution lines. The stand-alone memorydie 420 can be packaged and sold as a stand-alone memory device. Thisfeature is viewed as an advantage of the disclosed embodiments thatallows fabrication of the stand-alone memory die 430, in addition to themaster die 122 and the slave die 124, from the same starter die.

FIG. 4E illustrates a cross sectional view of the in-process memory die430 of FIG. 4D after further processing to form the master die 122according to an embodiment. The master die 122 is formed by fabricatingthe TSV 280 through the second metal 252(a) and the third metal 370(a).A portion of the third metal 370(b) forms the test pad 270 of FIGS. 2and 3. A portion of the third metal 370(a) couples to a portion of thesecond metal 252(a), and can therefore communicate to all of thecircuitries that are coupled to the second metal 252(a). In general,long distance interconnections and power distribution may be provided bythe third metal 370. In particular, the third metal 370(a) couples thecircuitries in the interface 260 of the master die 122 to the TSVs 280and provides power distribution wiring for high-speed testing of thememory die stack 160.

FIG. 4F illustrates a cross sectional view of an in-process memory diestack 450 after stacking the master die 122 of FIG. 4E and the slavedies 124 of FIG. 4C according to an embodiment. Except for the bottomslave die 124, which is kept intact for structural support, the masterdie 122 and other slave dies 124 are thinned sufficiently for the bottomof the TSVs 280 to be exposed, so that they can interconnect to oneanother in the stack configuration. In the memory die stack 450, eachslave die 124 has its interface 260 of FIG. 2 coupled to the TSV 280,and in the master die 122, the interface 260 is also coupled to the TSV280. Therefore, signals can travel between each of the slave dies 124and the connection pads 270 of FIG. 2, through the TSVs 280 and theinterface 260 of the master die 122.

The memory die stack 450 shows a portion of the memory die stack 160 ofFIG. 1, which when packaged forms the memory device 120 of FIG. 1. Aportion of the third metal 370(a) is connected to the TSV 280 to couplethe interface 260 of the master die 122 to core circuitries of the slavedies 124. Test pads 230 are accessible on the master die after assemblyof the memory die stack 160 to provide additional testing options. Amain advantage of the memory device 120 is revealed through carefulexamination of the formation steps of the memory dies of FIGS. 4B-4E andthe memory die stack 450. Specifically, the cost savings due to theelimination of the third metal in the slave dies 124 can be quiteconsiderable. In addition, the opportunity provided by the disclosedembodiments to fabricate the stand-alone memory die 430, the master die122, and the slave dies 124, using the starting die 420 is alsoadvantageous. Specifically, it allows significant cost savings using thesame lithographic masks and fabrication processes in the mass productionof the starting die 420, which then can be converted to any of themaster die 122, the slave dies 124, or the stand-alone memory die 430.

While the structures and methods described above lend themselves well toreducing costs associated with memory device metallization layers,further steps may be taken in some embodiments to reduce costsassociated with TSV formation. FIG. 5A illustrates a schematic diagramof a multiplexer circuit 500A used in a x16 stand-alone memory die 430of FIG. 4D according to an embodiment. As discussed above with respectto FIG. 1, a DRAM device may be known as a x4, x8, or x16 DRAM,depending on the number of data bits (e.g., 4 bits (x4), 8 bits (x8), or16 bits (x16)) that it provides at its output. The stand-alone memorydie 430 can be configured, for example, as a x16 memory device by usinga number of multiplexer circuits 500A. The multiplexer circuit 500Aincludes a multiplexer 510, a multiplexer 520, and four de-multiplexers530. The multiplexers 510 and 520 are 2-input and 4-input multiplexers,respectively, whereas each de-multiplexer 530 is a 2-outputde-multiplexer. One multiplexer circuit 500A is needed for four datalines connected to the array blocks 250 of FIG. 2. For example, in aDDR3 memory device, where 8 array data lines correspond to one externaldata line, a x16 DRAM that has 128 array data lines in total needs 32multiplexer circuits 500A. Address select signals 512 and 522 selectrouting from the inputs to one of the outputs of the multiplexers 510and 520, respectively. Similarly, address select signal 532 selectsrouting from the input to one of the outputs of the de-multiplexer 530.In the configuration shown in FIG. 5A, the address select signals 512,522, and 532 are asserted such that all 4 array bits 540 are coupledthrough the dotted-line routes to an interface circuit 550. The 4 arraybits 540 are provided at the edge of the array block 250 of FIG. 2. Theinterface circuit 550 is formed in the interface 260 of FIG. 2. Themultiplexers 510 and 520 are formed in one of the TSV stripes 240 andcoupled to the interface circuit 550 through the third metal 370 of FIG.3. In embodiments, the assertion of the address select signals 512, 522,and 532 can be configured during packaging of the memory die (e.g.,memory die 430) by using fuses or by hard bonding of respective pads.

FIG. 5B illustrates a schematic diagram of a multiplexer circuit 500Bused in a x8 stand-alone memory die 430 of FIG. 4D according to anembodiment. The stand-alone memory die 430, in this embodiment, isconfigured as a x8 memory device by asserting the address select signals512, 522, and 532 such that either the routes marked by broken-lines orthe routes marked by dotted-lines are selected to couple signals betweenthe 4-array bits 540 and the interface circuit 550, therefore providingpaths for two routes since in a x8 memory only half of the bits areneeded simultaneously. In embodiments, the assertion of the addressselect signals 512, 522, and 532 can be configured during packaging ofthe memory die (e.g., memory die 430) by using fuses or by hard bondingof respective pads.

FIG. 5C illustrates a schematic diagram of a multiplexer circuit 500Cused in a x4 stand-alone memory die 430 of FIG. 4D according to anembodiment. The stand-alone memory die 430, in this embodiment, isconfigured as a x4 memory device by asserting the address select signals512, 522, and 532 such that only one of the four differently-markedroutes are selected to couple signals between the 4 array bits 540 andthe interface circuit 550, therefore providing a path for only oneroute. The x4 memories may be more suitable for error correctionschemes, and their use may be more common in server DRAM applications.In embodiments, the assertion of the address select signals 512, 522,and 532 can be configured during packaging of the memory die (e.g.,memory die 430) by using fuses or by hard bonding of respective pads.

FIG. 5D illustrates a schematic diagram of multiplexer circuits 502 and504 used in the memory die stack 160 of FIG. 1 according to anembodiment. In the memory die stack 160, at any moment of time only oneof the memory dies (e.g., the master die 122 or the slave dies 124) maybe selected to communicate data to the interface circuit 550 of themultiplexer circuits 502. The selection of the communicating die isperformed by suitable configuration of the multiplexer circuits 502 and504. The multiplexer circuit 502 is formed on the master die 122,whereas the multiplexer circuit 504 is formed on each of the slave dies124. The multiplexer circuit 502 and the multiplexer circuit 504 arecoupled via the TSVs 280. Note that in the slave die 124, the interfacecircuit 550 is not accessible because it is not coupled to the secondand third metals 252 and 370, as discussed above with respect to FIG. 3.

As described below, the multiplexers of FIG. 5D allow providing one bitof output data from the four-die memory die stack 160 of FIG. 1, byusing only one TSV for every 4 array bits. Alternatively, should thememory dies of the memory die stack 160 be configured to couple to thememory controller 140 of FIG. 1 independently, via separate sets ofTSVs, four TSVs per four array bits would be needed. Therefore, the useof the multiplexers of FIG. 5D reduces the number of TSVs and thus addsto the cost savings described above with respect to metallizationlayers.

For selection of the master die 122 for communicating with the interface550, the multiplexer circuit 502 is configured similar to themultiplexer circuit 500C of FIG. 5C, and none of the address selectsignals 512, 522, or 532 of the multiplexer circuit 504 are asserted.For selection of one of the slave dies 124 for communicating with theinterface circuit 550, the address select signals 512, 522, or 532 ofmultiplexer circuit 504 are asserted such that only one of thedifferently-marked routes are selected to carry one bit of data from the4 array bits 540 to the TSVs 280. In addition, the address select signal512 of the multiplexer 510(a) is asserted to allow the bit of data totravel from the TSVs 280 to the interface circuit 550. In embodiments,the assertion of the address select signals 512, 522, and 532 can beconfigured during packaging of the memory die stack 160 by using fusesor by hard bonding of respective pads.

FIG. 6A illustrates a cross sectional view of a portion of the masterdie 122 with a connection to the TSV 280 through the third metal 370according to an embodiment. In this embodiment, similar to the masterdie 122 of FIG. 3, the connection to the TSV 280 of the circuitry in theinterface 260 is provided by the third metal 370. The interface 260 iscoupled to the second metal 252, which is in turn connected through avia 610 to the third metal 370. Depending on the position of the TSV 280with respect to the interface 260, a signal from the interface 260 tothe TSV 280 may have to travel a substantially long distance. In FIG.6A, the pad 270 shown to be coupled to the interface 260 comprises oneof the pads 270 of FIG. 2, which are positioned over the interface 260region (see FIG. 2).

FIG. 6B illustrates a cross sectional view of a portion of the masterdie 122 similar to the embodiment shown in FIG. 6A, but with aconnection to the TSV 280 through a re-driver circuit 650 according toan embodiment. In this embodiment, unlike the embodiment of FIG. 6A, inwhich the interface 260 is coupled to the TSV 280 via the third metal370, the coupling of the interface 260 to the TSV 280 is provided viathe second metal 252 and through a re-driver circuit 650 and onlypartially through the third metal 370. The advantage of this embodimentover the embodiment of FIG. 6A lies in the operational speed of thecoupling. Specifically, the embodiment of FIG. 6B provides a fastercoupling than that of FIG. 6A. The higher speed of the embodiment inFIG. 6B is due to reduction of the loading of the TSV by eliminating thesubstantially long route in the third metal 370 that a signal has totravel. In this embodiment, signals travel between the interface 260 andthe TSV 280 through the re-driver circuit 650, which can providebuffering and power amplification for the traveling signal, thereforeimproving the speed of the coupling.

FIG. 7 illustrates a block diagram of a computer system 700 using theDIMM 100 of FIG. 1 according to an embodiment. The system 700 includes aplurality of components, such as at least one central processing unit(CPU) 702; a power source 706, such as a power transformer, powersupply, or batteries; input and/or output devices, such as a keyboardand mouse 710 and a monitor 708; communication circuitry 712; a BIOS720; a level two (L2) cache 722; Mass Storage (MS) 724, such as ahard-drive; Dynamic Random Access Memory (DRAM) 120; and at least onebus 714 that connects the aforementioned components. These componentsare at least partially housed within a housing 716. Some components maybe consolidated together, such as the L2 cache 722 and the CPU 702. TheDRAM 120 includes one or more stacked memory dies 160 described above.

When received within a computer system via one or more computer-readablemedia, such data and/or instruction-based expressions of the abovedescribed circuits may be processed by a processing entity (e.g., one ormore processors) within the computer system in conjunction withexecution of one or more other computer programs including, withoutlimitation, net-list generation programs, place and route programs andthe like, to generate a representation or image of a physicalmanifestation of such circuits. Such representation or image maythereafter be used in device fabrication, for example, by enablinggeneration of one or more masks that are used to form various componentsof the circuits in a device fabrication process.

In the foregoing description and in the accompanying drawings, specificterminology and drawing symbols have been set forth to provide athorough understanding of the present invention. In some instances, theterminology and symbols may imply specific details that are not requiredto practice the invention. For example, any of the specific numbers ofbits, signal path widths, signaling or operating frequencies, componentcircuits or devices and the like may be different from those describedabove in alternative embodiments. Also, the interconnection betweencircuit elements or circuit blocks shown or described as multi-conductorsignal links may alternatively be single-conductor signal links, andsingle conductor signal links may alternatively be multi-conductorsignal links. Signals and signaling paths shown or described as beingsingle-ended may also be differential, and vice-versa. Similarly,signals described or depicted as having active-high or active-low logiclevels may have opposite logic levels in alternative embodiments.Component circuitry within integrated circuit devices may be implementedusing metal oxide semiconductor (MOS) technology, bipolar technology orany other technology in which logical and analog circuits may beimplemented. With respect to terminology, a signal is said to be“asserted” when the signal is driven to a low or high logic state (orcharged to a high logic state or discharged to a low logic state) toindicate a particular condition. Conversely, a signal is said to be“deasserted” to indicate that the signal is driven (or charged ordischarged) to a state other than the asserted state (including a highor low logic state, or the floating state that may occur when the signaldriving circuit is transitioned to a high impedance condition, such asan open drain or open collector condition). A signal driving circuit issaid to “output” a signal to a signal receiving circuit when the signaldriving circuit asserts (or deasserts, if explicitly stated or indicatedby context) the signal on a signal line coupled between the signaldriving and signal receiving circuits. A signal line is said to be“activated” when a signal is asserted on the signal line, and“deactivated” when the signal is deasserted. Additionally, the prefixsymbol “/” attached to signal names indicates that the signal is anactive low signal (i.e., the asserted state is a logic low state). Aline over a signal name (e.g., ‘<signal name>’) is also used to indicatean active low signal. The term “coupled” is used herein to express adirect connection as well as a connection through one or moreintervening circuits or structures. Integrated circuit device“programming” may include, for example and without limitation, loading acontrol value into a register or other storage circuit within the devicein response to a host instruction and thus controlling an operationalaspect of the device, establishing a device configuration or controllingan operational aspect of the device through a one-time programmingoperation (e.g., blowing fuses within a configuration circuit duringdevice production), and/or connecting one or more selected pins or othercontact structures of the device to reference voltage lines (alsoreferred to as strapping) to establish a particular device configurationor operation aspect of the device. The term “exemplary” is used toexpress an example, not a preference or requirement.

While the invention has been described with reference to specificembodiments thereof, it will be evident that various modifications andchanges may be made thereto without departing from the broader spiritand scope of the invention. For example, features or aspects of any ofthe embodiments may be applied, at least where practicable, incombination with any other of the embodiments or in place of counterpartfeatures or aspects thereof Accordingly, the specification and drawingsare to be regarded in an illustrative rather than a restrictive sense.

I claim:
 1. A memory die for use in a memory device comprising: a memorycore having memory cell arrays interconnected by first and seconddistribution lines; a first metal layer including the first distributionlines; a second metal layer including the second distribution lines; aninterface circuit including input/output (I/O) circuitry that is notcoupled to the memory core via any conductors on the memory die; andwherein the memory core is configured to couple to a master dieinterface circuit formed on a master memory die.
 2. The memory dieaccording to claim 1 wherein the memory die comprises a slave memory dieconfigured to communicate with a memory controller via a master memorydie, and wherein the memory die is incapable of communicating command ordata with the memory controller without the master memory die.
 3. Thememory die according to claim 2 wherein the slave memory die comprisesat least one through-silicon-via (TSV) formed to couple the memory coreof the slave memory die to the interface circuit of the master memorydie.
 4. The memory die according to claim 3 wherein the slave memory diereceives power via the at least one TSV.
 5. The memory die according toclaim 1 wherein the memory die comprises a slave memory die configuredto communicate with a memory controller via a buffer die, and whereinthe memory die is incapable of communicating command or data with thememory controller without the buffer die.
 6. The memory die according toclaim 1 wherein the memory die is of a predetermined width, and isformed with a number of through-silicon-vias, wherein the number ofthrough-silicon-vias is based on the predetermined width.
 7. The memorydie according to claim 1, wherein the memory die comprises at least onethrough-silicon-via (TSV) coupled to at least one of the first metallayer or the second metal layer, wherein the at least one TSV is notcoupled to the interface circuit via any conductors on the memory die.8. The memory die according to claim 1, wherein the interface circuitcomprises at least one of an input/output driver, an input/outputreceiver, a re-driver, a decoder, an ESD circuit, and a multiplexing anddata steering circuit.
 9. A memory device comprising: a master memorydie; and a slave memory die coupled to the master memory die in astacked configuration, wherein each of the master and slave memory diescomprises: memory core circuitry including memory cell arrays and firstand second distribution lines interconnecting the memory cell arrays; afirst metal layer including the first distribution lines; a second metallayer including the second distribution lines; and interface circuitry;wherein the master memory die is further formed with a third metal layerand the memory core circuitry of the slave memory die couples to theinterface circuitry of the master memory die via the third metal layeron the master memory die, and wherein the memory core circuitry of theslave memory die is not coupled to the interface circuitry of the slavememory die via any conductor formed on the slave memory die.
 10. Thememory device according to claim 9 wherein each of the master and slavedies further includes at least one through-silicon-via (TSV) formed tocouple the core memory circuitry of the slave memory die to theinterface circuitry of the master memory die.
 11. The memory deviceaccording to claim 10 wherein the third metal layer of the master memorydie is coupled to the at least one TSV of the slave memory die.
 12. Thememory device according to claim 9 wherein the interface circuitry ofthe slave memory die is decoupled from the first and second metal layersof the slave memory die.
 13. The memory device according to claim 9wherein the interface circuitry of the master memory die is configuredto communicate with a memory controller through the third metal layer.14. The memory device according to claim 9 wherein the third metal layercomprises a redistribution layer (RDL).
 15. The memory device accordingto claim 10 wherein the slave memory die receives power from the atleast one TSV formed on the slave memory die, and wherein the at leastone TSV is coupled to the third metal layer on the master memory die.16. A method of operating a memory die stack including a master memorydie and a slave memory die, comprising: selectively configuring a firstmultiplexer circuit included in the master memory die to provideselected one or more routes for data communication between array datalines of the master memory die and an interface circuit of the mastermemory die; selectively configuring a second multiplexer circuitincluded in the slave memory die to provide one or more selected routesfor data communication between array data lines of the slave memory dieand a through-silicon-via (TSV) coupled to the interface circuit of themaster memory die and; wherein the array data lines of the slave memorydie are selectively decoupled from I/O circuitry of the slave memory diewhen the array data lines are coupled to the interface circuit of themaster memory die.
 17. The method of claim 16, wherein configuring thefirst and second multiplexer circuits are performed by asserting a firstand a second set of address lines which control one or more multiplexersand de-multiplexers included in the respective first and secondmultiplexer circuits.
 18. The method of claim 17, further comprising,when the master memory die is selected, configuring the firstmultiplexer circuit but not asserting any of the address lines of thesecond set of address lines.
 19. The method of claim 17, furthercomprising, when the slave memory die is selected, configuring the firstmultiplexer circuit to connect only the TSV to the interface circuit andasserting the address lines of the second set of address lines toprovide for data communication between the array data lines of the slavememory die and the TSV.